1. Field of the Invention
The invention relates generally to an expansion tool and method adapted for use with oilfield pipes (“tubulars”). More specifically, the invention relates to an expansion tool used to plastically radially expand downhole tubular members in a wellbore.
2. Background Art
Casing joints, liners, and other oilfield tubulars are often used in drilling, completing, and producing a well. Casing joints, for example, may be placed in a wellbore to stabilize a formation and protect a formation against high wellbore pressures (e.g., wellbore pressures that exceed a formation pressure) that could damage the formation. Casing joints are sections of steel pipe, which may be coupled in an end-to-end manner by threaded connections, welded connections, and other connections known in the art. The connections are usually designed so that a seal is formed between an interior of the coupled casing joints and an annular space formed between exterior walls of the casing joints and walls of the wellbore. The seal may be, for example, an elastomer seal (e.g., an o-ring seal), a metal-to-metal seal formed proximate the connection, or similar seals known in the art.
In some well construction operations, it is advantageous to radially plastically expand threaded pipe or casing joints in a drilled (“open”) hole or inside a cased wellbore. Radially plastically expanding a pipe, as used in this application, describes a permanent expansion, or increase, of the inside diameter of a pipe or casing. The casing might experience some elastic recovery, where the diameter decreases slightly from the largest expanded diameter, but the final diameter will be permanently larger than the initial diameter. In a cased wellbore, radially expandable casing can be used to reinforce worn or damaged casing so as to, for example, increase a burst rating of the old casing, thereby preventing premature abandonment of the hole.
In conventional oilfield drilling, casing strings are installed at regular intervals throughout the drilling process. The casing for one interval is installed by lowering it through the casing for a previous interval. This means that the outer diameter of a casing string is limited by the inner diameter of previously installed casing strings. Thus, the casing strings in a conventional wellbore are nested relative to each other, with casing diameters decreasing in a downward direction with each interval.
An annular space is provided between each string of casing and the wellbore so that cement may be pumped into the annular space or annulus to seal between the casing and the wellbore. Because of the nested arrangement of the casing strings in a conventional wellbore and the annular space required around the casing strings for cement, the hole diameter required at the top of the wellbore may be relatively large. This large initial wellbore diameter leads to an increased expense of drilling large diameter holes and the added expense of cementing a large casing string. In addition, the nested arrangement of the casing strings in a conventional wellbore can severely limit the inner diameter of the final casing string at the bottom of the wellbore, which restricts the potential production rate of the well.
It is desirable that a casing string can be plastically radially expanded in situ (i.e., in place in the well) after it has been run into the wellbore through the previous casing string. This minimizes the reduction of the inner diameter of the final casing string at the bottom of the wellbore. Plastically radially expanding a casing string in the wellbore has the added benefit of reducing the annular space between the drilled wellbore and the casing string, which reduces the amount of cement required to effect a seal between the casing and the wellbore.
Various techniques to expand casing have already been developed. One technique uses an expansion tool, called a “pig,” which has a diameter that is larger than the inside diameter of the casing string. The tool is typically moved through a string of casing or tubing to plastically radially expand the string from an initial condition (e.g., from an initial diameter) to an expanded condition (e.g., to a final diameter). One common prior-art expansion process uses a conically tapered, cold-forming expansion tool to expand casing in a wellbore. The expansion tool is generally symmetric about its longitudinal axis. The expansion tool also includes a cylindrical section having a diameter typically corresponding to a desired expanded inside diameter of a casing string. The cylindrical section is followed by a tapered section.
The expansion tool is placed into a launcher at the bottom of the expandable casing string. The launcher is a belled section, threaded at one end and sealed off on the distal end with a cementing port in the bottom. The expansion tool is sealed inside the launcher and the launcher is made-up on the end of the expandable casing string. The casing string is set in place in the hole, usually by hanging-off the casing string from a casing hanger. Then, a working string of drillpipe or tubing is run into the wellbore and attached to the expansion tool (e.g., the working string is generally attached to the leading mandrel). The expansion tool may also comprise an axial bore therethrough so that pressurized fluid (e.g., drilling fluid) may be pumped through the working string, through the expansion tool, and into the wellbore so as to hydraulically pressurize the wellbore. Hydraulic pressure acts on a piston surface defined by a lower end of the expansion tool, and the hydraulic pressure is combined with an axial upward lifting force on the working string to force the expansion tool upward through the casing string so as to outwardly radially displace the casing string to a desired expanded diameter.
In a variation of this method, as the launcher just clears the casing shoe of the parent casing, the casing is expanded while the expansion tool is held still in space. The casing is simultaneously expanded and driven into the hole.
Alternatively, an expansion tool is mounted on the end of a long hydraulic cylinder. The cylinder and tool are run into the hole with the expandable casing suspended below on a hanger. The cylinder pushes the expansion tool into the casing string, making the liner hanger. The hydraulic cylinder and internal slip are retracted, the slips are reset in a new position, and the hydraulic cylinder is extended again. The process is repeated until the entire string is expanded.
In another method known in the art, the expansion tool has three retractable, angled rollers arrayed around the outside of the tool. The expandable casing is lowered into the hole on a set of clips carried above the expansion tool. At depth, the tool is rotated and pressure is slowly applied to the tool, causing the rollers to move radially outwards. The tool is then pushed or pulled through the casing while rotating.
Radial expansion may be performed at rates of, for example, 25 to 60 feet per minute. Other expansion processes, such as expansion under localized hydrostatic pressure, or “hydroforming,” are known in the art, but are generally not used as much as the cold-forming expansion process.
FIG. 1 shows a sectional drawing of a typical prior art conical expansion tool 100 (or “expansion pig”) beginning to deform casing pipe 117. The end 112 of the casing string 117 contacts the expansion tool 100 on a frustoconical expansion surface 105 of the tool 100. As the expansion tool 100 moves in the direction of travel 104, it will pass through the casing string 117, plastically radially expanding the casing string 117 as it moves.
The expansion tool 100, symmetric about centerline 103, has a cylindrical section 110, the diameter of which is about the same as the desired expanded diameter for the casing string 117. Typically, the expanded casing will recoil slightly from the diameter of the cylindrical section 110, and thus, the final expanded diameter of the casing 117 will be slightly less than the outer diameter of the cylindrical section 110. At the back end, the expansion tool 100 has a tapered section 111 that falls away from the cylindrical section 110.